National Transportation Safety Board spokesman Peter Knudson says the helicopter was headed toward Midwest National Air Center near Mosby, about 20 miles northeast of Kansas City, when it crashed about 7 p.m. Friday.
The helicopter was owned by Air Methods Corp., an air ambulance operator based in Englewood, Colo. The company plans a news conference Saturday to provide more details.
Officials say a 58-year-old female patient, a pilot and two medical workers died in the crash. The pilot had reported the helicopter was running low on fuel, but investigators say it could be months before the cause of the crash is known.
